* Step.init() now takes an options struct
* Step.init() now captures a small stack trace and stores it in the
Step so that it can be accessed when printing user-friendly debugging
information, including the lines of code that created the step in
question.
Usage of `catch unreachable` in build scripts is completely harmless
because build scripts are always run in Debug mode, however, it sets a
poor example for beginners to learn from.
